Taken alone, these words from the first chapter of Isaiah (10-17) don’t seem correct. Doesn’t God always listen to prayer? Well, the run up to this is very important (always remember the maxim “any text without a context is pretext for a prooftext” when folks are tossing around Scripture quotes). Just before these words, God rails against the wickedness of the people following ritual prescriptions but not living the Law. Afterwards He speaks these ominous words:
Your hands are full of blood!
Then, immediately, He gives the prescription for authentically approaching Him:
Put away your misdeeds from before my eyes;
cease doing evil; learn to do good.
Make justice your aim: redress the wronged,
hear the orphan’s plea, defend the widow.
The Responsorial Psalm (Ps 50:8-9, 16bc-17, 21 and 23) reinforces this command:
Why do you recite my statutes,
and profess my covenant with your mouth,
Though you hate discipline
and cast my words behind you?…
He that offers praise as a sacrifice glorifies me;
and to him that goes the right way I will show the salvation of God.
Efficacious prayer does not require perfection or we would all be doomed. What the Lord asks of us is sincere repentance and a firm purpose of amendment (which we should also pray for). Unthinking rituals and fulfilling the basic requirements, thinking that these are a “Get Out of Jail Free” card, while obstinately clinging to sin (especially sins that are mortal) and vice are the recipe for eternal disaster. We are to “cease doing evil,” to love “discipline,” and to not “cast [God’s] words behind” as we “offer praise [that] glorifies” God.